1. Field of the Invention
The present invention relates to a charging voltage measuring device and an ion beam irradiating device having a charging voltage measuring device which is employed in a process or apparatus for making ion implantation, ion doping or plasma treatment on a substrate, or a process or apparatus for conveying or drying the substrate, in which there is a fear that the surface of the substrate is electrified.
2. Description of the Related Art
In a process or apparatus having a fear that the surface of the substrate is electrified, it is important to measure a charging voltage on a substrate surface to prevent dielectric breakdown on the substrate surface.
In a specific apparatus employing an electrostatic chuck on the substrate holding unit for holding the substrate, a technique for acquiring a potential on the substrate surface from an adsorption current flowing through the electrodes of the electrostatic chuck has been offered (refer to JP-A-9-54130 (paragraph number 0010 to 0014, FIG. 1) and JP-A-10-27566 (paragraph number 0010 to 0015, FIG. 1) in the related-art, though this technique is not applicable when the electrostatic chuck is not employed.
Referring to FIGS. 1 and 2, a related-art typical charging voltage measuring method employing no electrostatic chuck will be described below by way of example.
First of all, when a substrate 6 is treated, a measuring electrode 8 is not provided, the substrate 6 to be treated is held and secured on a substrate holding unit 4 by a damper (not shown), and irradiated with an ion beam 2. In this way, the substrate 6 is treated with the ion implantation and ion doping.
The substrate holding unit 4 is a metallic plate, for example. The substrate 6 is a glass substrate for liquid crystal display, for example, but may be a semiconductor substrate or the like.
If the ion beam 2 is applied onto the substrate 6, the surface of the substrate 6 is electrified (charged up) due to positive charges of ions in the ion beam 2. Especially when the substrate 6 has an insulating property (electrical insulating property), the surface of the substrate 6 is more likely to be electrified. The glass substrate and the semiconductor substrate having an insulating layer on the surface are exemplary. At this time, the charging voltage on the substrate surface is simply decided by the balance between ions radiated as the ion beam 2 and electrons supplied to the substrate 6 along with the ion beam 2. The electrons may be those in a plasma existing around the ion beam 2 or those being supplied from an electron supply source as will be described later.
In order to measure the charging voltage on the surface of the substrate 6 as above described, a metallic measuring electrode 8 was placed closely on the surface of the substrate 6, and the ion beam 2 was applied onto the measuring electrode to measure the voltage of the measuring electrode 8 by a voltmeter 10, whereby the measured voltage was regarded as the charging voltage on the substrate surface. When the substrate 6 was actually treated by applying the ion beam 2 thereto, the measuring electrode 6 as an obstacle was removed.
With the related-art measuring method as above described, it is required to place the measuring electrode 8 on the surface of the substrate 6, whereby the charging voltage on the surface of the substrate 6 cannot be measured during the actual treatment (e.g., ion implantation).
Also, in measuring the charging voltage, the ion beam 2 is applied onto the metallic measuring electrode 8, whereby the charging voltage on the substrate surface is not correctly measured due to a difference in the material between the surface of the substrate 6 and the surface of the measuring electrode 8.